Plasma deposition method and system

ABSTRACT

There is provided a deposition technique wherein the amounts of eliminated F and H are small in the deposition of an insulating film, such as an SiOF film or an SiCHO film, which contains silicon, oxygen and other components and which has a lower dielectric constant than the dielectric constant of a silicon oxide film.  
     A plasma processing system for producing plasma with the energy of a power applied between first and second electrodes which are provided in a vacuum vessel so as to face each other in parallel and which are connected to separate high-frequency power supplies, respectively, is used. An object to be processed, e.g., a semiconductor wafer is mounted on the first electrode. The frequency of the high-frequency power applied to the first electrode is set to be in the range of from 2 MHz to 9 MHz, and the frequency of the high-frequency power applied to the second electrode is set to be 50 MHz or higher, to deposit an insulating film on the wafer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of The Invention

[0002] The present invention relates generally to a method and systemfor depositing an insulating film having a low dielectric constant of asilicon oxide film to which a predetermined material is added.

[0003] 2. Description of The Prior Art

[0004] As a conventional interlayer dielectric film of a device, asilicon oxide film (SiO₂ film) has been used. As one of techniques fordepositing an SiO₂ film, there is a method using a parallel plate plasmaprocessing system for applying a high-frequency power between top-andbottom electrodes, which are parallel to each other, to produce plasmato deposit a thin film with the plasma. As the prior art using thissystem, there is, e.g., Japanese Patent No. 2,774,367. This patentdisclose that the frequency of a high-frequency power supply connectedto the top electrode is set to be 100 MHz or higher, and the frequencyof a high-frequency power supply connected to the bottom electrode isset to be in the range of from 10 MHz to 50 MHz, to apply a highfrequency power between both electrodes to produce the plasma of asilane containing gas and oxygen gas to deposit an SiO₂ film.

[0005] In recent years, in order to further accelerate the operation ofdevices, it is required that the dielectric constant (relativedielectric constant) of an interlayer dielectric film is lowered. Thedielectric constant (relative dielectric constant) of an SiO₂ filmhaving been conventionally used is about 0.4 which can not cope withsuch a request, so that it is desired that an insulating film having alow dielectric constant is provided. Therefore, the inventor has studiedinsulating films which contain an SiO₂ film as an principal componentand other components and which has a lower dielectric constant than theSiO₂ film, e.g., SiOF films containing fluorine (F) and SiCHO filmscontaining carbon (C) and hydrogen (H).

[0006] However, if an insulating film of this type is deposited by theabove described prior art method, there is a problem in that a largeamount of the other components are eliminated from the film during aheat treatment which will be carried out later with respect to asemiconductor wafer. For example, if F is eliminated from the SiOF film,a metal wiring is corroded , and if H (hydrogen) is eliminated from theSiCHO film, H is accumulated between the SiCHO film and the metalwiring, so that the metal wiring is peeled off. It is guessed that thereason for this is that the energy of ions is too small to decrease thenumber of dangling bonds (unbonded hands), so that the other components(mixed components), such as F mixed in the SiO₂ film, are easilyeliminated.

SUMMARY OF THE INVENTION

[0007] It is therefore an object of the present invention to eliminatethe aforementioned problems and to provide a plasma deposition methodand system capable of depositing a high quality insulating film having alow dielectric constant.

[0008] In order to accomplish the aforementioned and other objects,according to one aspect of the present invention, a method and systemfor depositing a silicon oxide film is provided, which contains apredetermined material having a lower dielectric constant than thedielectric constant of a silicon oxide film (SiO₂ film), on an object tobe processed, using a so-called parallel plate plasma processing system,wherein the frequency of a high-frequency power applied to a firstelectrode, on which the object to be mounted, is set to be in the rangeof from 2 MHz to 9 MHz, and the frequency of a high-frequency powerapplied to a second electrode is set to be 50 MHz or higher. As thesilicon oxide film containing the predetermined material, there are Fcontaining films (SiOF films), C and H containing films (SiCHO films),and C, H and N containing films (SiCHNO films). According to the presentinvention, since the energy of ions during processing has a moderatemagnitude, the eliminated amount of the predetermined material is small,and the network bonds are sufficiently formed in the film, so that it ispossible to obtain a high quality insulating film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be understood more fully from thedetailed description given herebelow and from the accompanying drawingsof the preferred embodiments of the invention. However, the drawings arenot intended to imply limitation of the invention to a specificembodiment, but are for explanation and understanding only.

[0010] In the drawings:

[0011]FIG. 1 is a sectional view showing the whole construction of apreferred embodiment of a plasma processing system according to thepresent invention;

[0012]FIG. 2 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to a bottomelectrode (a first electrode) and the amount of F eliminated from anSiOF film;

[0013]FIG. 3 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the bottomelectrode and the etch rate of the SiOF film;

[0014]FIG. 4 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the bottomelectrode and the self-bias of the bottom electrode;

[0015]FIG. 5 is an illustration for explaining the self-bias;

[0016]FIG. 6 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to a topelectrode (a second electrode) and the etch rate of the SiOF film;

[0017]FIG. 7 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the topelectrode and the self-bias of the top electrode;

[0018]FIG. 8 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the bottomelectrode and the amount of H eliminated from an SiCHO film;

[0019]FIG. 9 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the bottomelectrode and the etch rate of the SiCHO film;

[0020]FIG. 10 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the bottomelectrode and the amount of H eliminated from an SiCHNO film;

[0021]FIG. 11 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the bottomelectrode and the etch rate of the SiCHNO film;

[0022]FIG. 12 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the bottomelectrode and the amount of H eliminated from the SiCHNO film; and

[0023]FIG. 13 is a characteristic diagram showing the relationshipbetween the frequency of a high-frequency power applied to the bottomelectrode and the etch rate of the SiCHNO film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Referring now to the accompanying drawings, particularly to FIG.1, a preferred embodiment of a plasma deposition system according to thepresent invention will be described below.

[0025] This plasma deposition system has a grounded cylindrical vacuumvessel 1 made of, e.g., aluminum. On the bottom of the vacuum vessel 1,a susceptor 2 is provided for supporting thereon an object to beprocessed, e.g., a semiconductor wafer, (which will be hereinafterreferred to as a wafer). The susceptor 2 also serves as a bottomelectrode which is a first electrode of parallel plate electrodes. Thesusceptor 2 is made of, e.g., aluminum, and has a substantiallycylindrical shape. On the surface of the susceptor 2, an electrostaticchuck 3 is provided. The electrostatic chuck 3 comprises a chuckelectrode 31 embedded in a thin dielectric layer. When a dc voltage isapplied to the chuck electrode 31 from a dc voltage source 33 via aswitch 32, the chuck electrode 31 electrostatically absorbs a wafer W.The electrostatic chuck 3 has a plurality of a heat-transferring holes34 through which a heat-transferring gas, e.g., helium gas, is suppliedfrom a heat-transferring gas supply pipe 35 to a fine gap between thewafer and the electrostatic chuck 3. A lifter pin (not shown) capable ofpassing through the electrostatic chuck 3 and the susceptor 2 to movevertically is provided for delivering the wafer W.

[0026] In the susceptor 2, a refrigerant passage 21 is formed so that arefrigerant supplied from a refrigerant supply pipe 22 passes throughthe refrigerant passage 21 to be discharged from a refrigerant dischargepipe 23. The temperature of the wafer W is controlled by, e.g., thetemperature of the refrigerant and the efficiency of heat transferbetween the wafer W and the electrostatic chuck 3 due to theheat-transferring gas. On the peripheral edge portion of the top of thesusceptor 2, a ring body 24 of an insulating material is provided foreffectively causing reactive ions to enter the wafer W.

[0027] The susceptor 2 is inserted into an opening, which is formed inthe top face of a flat cylindrical insulator body 25, so as to beisolated from the vacuum vessel 1. A matching device 41 and a firsthigh-frequency power supply 4 are provided between the susceptor 2,which is the bottom electrode (first electrode), and a referencepotential, e.g., the earth. The frequency of the first high-frequencypower supply 4 is set to be a predetermined frequency of, e.g., 2 MHz to9 MHz.

[0028] On the ceiling portion of the vacuum vessel 1, an electrode plate51 forming the top electrode serving as the second electrode is providedso as to face the susceptor 2 in parallel. The electrode plate 51 isformed of, e.g., aluminum coated with SiO₂, and has a large number ofgas supply holes 52. The electrode plate 51 is supported on an electrodesupporting body 53 of a conductive material. Between the electrode plate51 and the electrode supporting body 53, a gas diffusing plate 54 isarranged, and a gas supply pipe 6 is connected to the electrodesupporting body 53 for supplying a process gas to a space between theelectrode supporting body 53 and the gas diffusing plate 54, so that theprocess gas from the gas supply pipe 6 is supplied to a process spacefrom the gas supply holes 52 of the electrode plate 51 via the gasdiffusing plate 54. The electrode plate 51 and the electrode supportingbody 53 are isolated from the vacuum vessel 1 by means of an insulator55.

[0029] Between the electrode plate 51 serving as the top electrode(second electrode) and the reference potential, e.g., the earth, amatching device 71 and a second high-frequency power supply 7 areprovided. The frequency of the second high-frequency power supply 7 isset to be, e.g., 50 MHz or higher, e.g., 60 MHz.

[0030] The gas supply pipe 6 is divided into a plurality of branchingpassages, each of which is connected to a process gas source. In thispreferred embodiment, in order to deposit an SiOF film, four branchingpassages 61A through 61D are connected to gas supply sources 62A through62D for supplying silicon tetrafluoride (SiF₄) gas, monosilane (SiH₄)gas, oxygen (O₂) gas and argon (Ar) gas, respectively. Furthermore, MAthrough MD denote flow control parts (mass flow controllers), and Vdenotes a valve.

[0031] As the exhaust system of the vacuum vessel 1, an exhaust pipe 11is connected to the bottom of the vacuum vessel 1 to evacuate theinterior of the vacuum vessel 1 by means of a vacuum pump 12.

[0032] The operation of the above described preferred embodiment will bedescribed below.

[0033] The wafer W serving as an object to be processed is introducedfrom a load-lock chamber (not shown), which is adjacent to the vacuumvessel 1, into the vacuum vessel 1 which has been held at apredetermined degree of vacuum. Then, the wafer W is mounted on thesusceptor 2, which has been adjusted at a predetermined temperature, bythe vertical movement of the lifter pin (not shown). Then, the switch 32is turned on to apply a dc voltage to the chuck electrode 31, so thatthe wafer W is fixed by the electrostatic chuck 3. Subsequently, thevalve V is open to first supply the flow rate of a gas which does notcontribute to a deposition reaction by itself, e.g., O₂ gas, to thevacuum vessel 1 from the gas supply source 62C via the gas supply pipe 6and the gas supply holes 52 while the flow control part MC controls theflow rate of the gas.

[0034] Then, the second high-frequency power supply applies ahigh-frequency power having a power value of 2.7 kW and a predeterminedfrequency of 50 MHz or higher, e.g., 60 MHz, between the secondelectrode (electrode plate) 51 and the earth. Thereafter, e.g., after 1to 2 minutes, SiF₄ gas, SiH₄ gas and Ar gas are supplied to the vacuumvessel 1 from the gas supply holes 52 via the gas supply pipe 6 whilethe flow rates of these gases are controlled by the flow control partsMA, MB and MD, respectively, and the first high-frequency power supply 4applies a high-frequency power having a power value of, e.g., 0.3 kW,and a frequency of 2 MHz to 9 MHz, e.g., 8 MHz, between the firstelectrode (susceptor) 2 and the earth.

[0035] As a result, the high-frequency power is applied between thefirst electrode 2 and the second electrode 51, and its energy producesthe plasma of the above described gases to deposit an SiOF film on thewafer W. The SiOF film is a film wherein F enters SiO₂ serving as aprincipal component, and which has a dielectric constant of 3.5 which issmaller than the dielectric constant of an SiO₂ film. Furthermore, whenO₂ gas is introduced, other gases, such as Ar and N₂ gases, togetherwith O₂ gas, may be introduced, but it is required that no film isdeposited with these gases.

[0036] As described above, the reason why the high-frequency power isapplied to the first electrode 2 after the high-frequency power isapplied to the second electrode 51 is as follows. If the high-frequencypower is first applied to the first electrode 2, ions enter the wafer Wto be sputtered. Therefore, the high-frequency power is first applied tothe second electrode 51, and after the time required for plasma to bestable and for the temperature of the wafer W to rise to a predeterminedtemperature, the high-frequency power is applied to the first electrode2.

[0037] As an example of process conditions, the flow rates of SiF₄ gas,SiH₄ gas, O₂ gas and Ar gas are set to be 28 sccm, 22 sccm, 250 sccm and50 sccm, respectively, and the pressure in the vacuum vessel 1 is set tobe 1.3 Pa (10 mTorr).

[0038] In this preferred embodiment, the frequency of the high-frequencypower applied to the bottom electrode (susceptor 2) serving as the firstelectrode, on which the wafer W is supported, is in the range of from 2MHz to 9 MHz, so that the energy of ions during deposition has amoderate magnitude which is not too large and not too small as will bedescribed later. Therefore, the amount of F eliminated from the SiOFfilm during the subsequent heat process is suppressed, if the SiOF filmis applied to the interlayer dielectric film, the corrosion of the metalwiring is suppressed. In addition, since the frequency of thehigh-frequency power applied to the top electrode (electrode plate 51)serving as the second electrode is set to be 50 MHz or higher, the topelectrode 51 can be inhibited from being sputtered as will be describedlater, so that it is possible to decrease the contamination of the SiOFfilm by the sputtering component of the top electrode 51.

[0039] In addition, SiO₂ may be used as a principal component, and C andH may be mixed therein as other components. In this case, an SiCHO filmis obtained. In order to deposit a film of this type, an alkylsilane gas[Si(C_(n)H_(2n+1))_(m)H_(4-m)] and oxygen gas serving as raw materialgases may be reacted with each other. The alkylsilane gases includemethylsilane gases, such as monomethylsilane gas [SiH₃CH₃],dimethylsilane gas [SiH₂(CH₃)₂], trimethylsilane gas [SiH(CH₃)₃] andtetrasilane gas [Si(CH₃)₄], and ethylsilane gas. In place of alkylsilanegases, alkoxysilane gas, such as CH₃Si(OCH₃)₃, may be used, or thesegases may be mixed to be used.

[0040] The other components may be C, H and N. In this case, an SiCHNOfilm is obtained. In order to deposit a film of this type, analkylsilane gas such as methylsilane gas, alkoxysilane gas, oxygen gasand nitrogen gas (N₂ gas) may be reacted with each other. In the placeof N₂ gas, nitrogen oxide gas, dinitrogen oxide gas, nitrogen tetraoxide gas or ammonia gas may be used, or these gases may be mixed to beused. The dielectric constant of the film thus obtained by adding N tothe SiCHO film is slightly increased by the addition of N. However, thisfilm is suitable for, e.g., an interlayer dielectric film of a deviceusing a Cu wiring, since it has the diffusion inhibiting effect on Cuand the anti-hygroscopic property enhancing effect (the water confiningeffect).

EXAMPLES Example 1

[0041] On the process conditions in the above described preferredembodiment, the frequency f1 of the high-frequency power applied to thebottom electrode 2 was set to be 1 MHz, 2 MHz, 4 MHz, 6 MHz, 8 MHz, 9MHz, 10 MHz and 13.56 MHz to deposit thin films. With respect to thethin films thus obtained, the amount of eliminated F (the amount ofdegassing) was examined, so that the results shown in FIG. 2 wereobtained. The amount of eliminated F was examined by the TDS spectrum(Thermal Desorption Spectroscopy). Each of the SiOF films was etchedwith 10 wt. % HF solution (hydrofluoric acid solution) to examine etchrates, so that the results shown in FIG. 3 were obtained. The units ofthe eliminated amounts and etch rates of the SiOF films are arbitrary.

[0042] From the results shown in FIGS. 2 and 3, it can be seen that whenthe frequency f1 is in the range of from 2 MHz to 9 MHz, the amount ofeliminated F is small, and the etch rate is slow, so that a compact andhigh quality SiOF film having strong bonds can be obtained. It isconsidered that the reason for this is that if the frequency f1 is lowerthan 2 MHz, the energy of ions in plasma is too great, so that thenetwork bonds of the respective atoms, particularly Si—F or O—F bond,are cut so that F exists in the film in an unstable state. It isconsidered that the phenomenon that bonds in the film are cut is causedmainly by the influence of the collision energy of argon ions. On theother hand, it is considered that if the frequency f1 exceeds, theenergy of ions in plasma is too small, so that F exists in the film inan unstable state without being sufficiently bonded. Therefore, if thefrequency f1 is beyond the range of from 2 MHz to 9 MHz, it is guessedthat the film is porous, F is easily eliminated, and the etch rateincreases.

[0043] When the thin films were deposited at the respective frequenciesf1 as described above, the value of the self-bias of the bottomelectrode 2 was examined, so that the results shown in FIG. 4 wereobtained. This self-bias is obtained by providing an oscilloscopebetween the bottom electrode 2 and the earth and by obtaining adifferential voltage Vdc between the voltage waveform (solid line) ofthe first high-frequency power supply 4 and the voltage waveform (dottedline) appearing at the oscilloscope as shown in FIG. 5. As can be seenfrom FIG. 4, Vdc increases as the frequency decreases, and it is veryhigh if the frequency is lower than 2 MHz, so that it is supported thatthe collision energy of ions is too great. In view of the foregoing, thefrequency f1 of the high-frequency power applied to the bottom electrode2 must be in the range of from 2 MHz to 9 MHz.

[0044] On the process conditions in the above described preferredembodiment, the high-frequency power was not applied to the bottomelectrode 2, i.e., the power of the first high-frequency power supply 4was set to be zero, and the frequency f2 of the top electrode 51 was setto be 13.56 MHz, 27 MHz, 50 MHz, 60 MHz and 100 MHz to similarly examinethe etch rate and the magnitude of self-bias (Vdc) of each of SiCF filmsevery frequency, so that the results shown in FIGS. 6 and 7 wereobtained. If the frequency f2 is lower than 50 MHz, the etch rate ishigh as can be seen from FIG. 6, and Vdc is high as can be seen fromFIG. 7. It is considered that this means that if the frequency f2 islower than 50 MHz, the energy of ions increases to sputter the topelectrode 51, so that its sputtered substance is incorporated into theSiOF film to serve as contamination. That is, it is considered that thesputtered substance, which is an impurity flying from the top electrode51, is incorporated into the SiOF film to serve as contamination. Thatis, if the sputtered substance, which is the impurity flying from thetop electrode 51, is incorporated into the SiOF film, the impurityexists in a non-network bond state, so that the film is porous andbrittle. Therefore, it is required that the frequency f2 of thehigh-frequency power applied to the top electrode 51 is 50 MHz orhigher.

Example 2

[0045] As deposition gases, dimethylsilane gas (SiH₂(CH₃)₂) and O₂ gaswere used, and their flow rates were set to be 50 sccm and 250 sccm,respectively. Other conditions were the same as those in the abovedescribed Example 1, and the frequency of the high-frequency powerapplied to the bottom electrode 2 was set to be the same eightfrequencies as those in Example 1 to deposit thin films on wafers. Thethin films thus obtained are SiCHO films wherein C and H are mixed inSiO₂ serving as a principal component. With respect to each of the thinfilms, the amount of degassed H and the etch rage due to hydrofluoricacid solution were examined similar to Example 1, so that the resultsshown by mark ◯ in FIGS. 8 and 9.

Example 3

[0046] SiCHO films were deposited on wafers in the same manner as thatin above described Example 2, except that alkoxysilane gas(CH₃Si(OCH₃)₃) was used in place of SiH₂(CH₃) gas. With respect to eachof the thin films, the amount of degassed H and the etch rate due tohydrofluoric acid solution were similarly examined, so that the resultsshown by mark Δ in FIGS. 8 and 9.

Example 4

[0047] In addition to the gas used in the above described Example 2, N₂gas was used as a deposition gas, and the flow rate of N₂ gas was set tobe 50 sccm to deposit thin films on wafers in the same manner as that inExample 2. The thin films thus obtained are SiCHNO films wherein N isadded to the SiCHO film obtained in Example 2. With respect to each ofthe thin films, the amount of degassed H and the etch rate due tohydrofluoric acid solution were similarly examined, so that the resultsshown by mark ◯ in FIGS. 10 and 11.

Example 5

[0048] In addition to the gas used in the above described Example 3, N₂gas was used as a deposition gas, and the flow rate of N₂ gas was set tobe 50 sccm to deposit SiCHNO films on wafers in the same manner as thatin Example 2. With respect to each of the thin films, the amount ofdegassed H and the etch rate due to hydrofluoric acid solution weresimilarly examined, so that the results shown by mark Δ in FIGS. 10 and11.

Example 6

[0049] As deposition gases, SiH₂(CH₃)₂ gas and N₂O gas were used, andtheir flow rates were set to be 50 sccm and 50 sccm, respectively, todeposit SiCHNO films on wafers in the same manner as that in Example 2.With respect to each of the thin films, the amount of degassed H and theetch rate due to hydrofluoric acid solution were similarly examined, sothat the results shown by mark ◯ in FIGS. 12 and 13.

Example 7

[0050] As deposition gases, CH₃Si(OCH₃)₃ gas and N₂O gas were used, andtheir flow rates were set to be 50 sccm and 50 sccm, respectively, todeposit SiCHNO films on wafers in the same manner as that in Example 2.With respect to each of the thin films, the amount of degassed H and theetch rate due to hydrofluoric acid solution were similarly examined, sothat the results shown by mark Δ in FIGS. 12 and 13.

[0051] As can be seen from the results in Examples 2 through 7, when thefrequency f1 is in the range of from 2 MHz to 9 MHz, the amount ofeliminated H is small, and the etching rate is low, so that it ispossible to obtain compact, high quality films having strong bonds. Withrespect to the influence of the frequency f2 of the high-frequency powerapplied to the top electrode 51, any experiments have not particularlybeen carried out. However, it is not feared there is no bad influence onthe film if the frequency f2 is set to be 50 MHz similar to Example 1since there is a problem in the sputtered substance of the top electrodeis mixed in the film.

[0052] According to the present invention, by using a so-called parallelplate plasma processing system, it is possible to deposit a high qualityinsulating film having a low dielectric constant, so that it is possibleto contribute to the improvement of, e.g., the operating speed of adevice.

[0053] While the present invention has been disclosed in terms of thepreferred embodiment in order to facilitate better understandingthereof, it should be appreciated that the invention can be embodied invarious ways without departing from the principle of the invention.Therefore, the invention should be understood to include all possibleembodiments and modification to the shown embodiments which can beembodied without departing from the principle of the invention as setforth in the appended claims.

What is claimed is:
 1. A plasma deposition method for carrying out aplasma deposition using a plasma processing system comprising a vacuumvessel, first and second electrode which are provided in the vacuumvessel and which face each other in parallel, and first and secondhigh-frequency power supplies capable of applying high-frequency powershaving different frequencies to the respective electrodes, respectively,wherein a predetermined deposition gas is introduced into a spacebetween said electrodes, and a high-frequency power having apredetermined frequency selected from the range of from 2 MHz to 9 MHzand a high-frequency power having a predetermined frequency selectedfrom the range of 50 MHz or higher are applied to said first and secondelectrodes, respectively, to produce plasma to deposit a silicon oxidefilm, which contains a predetermined material having a lower dielectricconstant than the dielectric constant of a silicon oxide film, on anobject to be processed, which is mounted on said first electrode.
 2. Aplasma deposition method for carrying out a plasma deposition using aplasma processing system comprising a vacuum vessel, first and secondelectrode which are provided in the vacuum vessel and which face eachother in parallel, and first and second high-frequency power suppliescapable of applying high-frequency powers having different frequenciesto the respective electrodes, respectively, said method comprising thesteps of: mounting an object to be processed, on said first electrode;introducing a gas containing at least oxygen into said vacuum vessel;applying a high-frequency power having a predetermined frequencyselected from the range of 50 MHz or higher, to said second electrode;thereafter, introducing a deposition gas containing at least silicon anda predetermined material to be added, into said vacuum vessel, andapplying a high-frequency power having a predetermined frequencyselected from the range of from 2 MHz to 9 MHz, to said first electrode;and depositing a silicon oxide film, which contains a predeterminedmaterial having a lower dielectric constant than the dielectric constantof a silicon oxide film, on said object with the applied high-frequencypowers.
 3. A plasma deposition method as set forth in claim 1 or 2,wherein said predetermined material to be added contains fluorine.
 4. Aplasma deposition method as set forth in claim 1 or 2, wherein saidpredetermined material to be added contains carbon and hydrogen.
 5. Aplasma deposition method as set forth in claim 4, wherein saidpredetermined material to be added further contains nitrogen.
 6. Aplasma deposition method as set forth in claim 1 or 2, wherein saiddeposition gas contains at least one of an alkylsilane gas andalkoxysilane gas, and hydrogen gas.
 7. A plasma deposition method as setforth in claim 6, wherein said deposition gas further contains any oneof nitrogen gas, nitrogen oxide gas, dinitrogen oxide gas, nitrogentetra oxide gas and ammonia gas.
 8. A plasma deposition system, whichcomprising, a vacuum vessel, first and second electrode which areprovided in the vacuum vessel and which face each other in parallel, andfirst and second high-frequency power supplies capable of applyinghigh-frequency powers having different frequencies to the respectiveelectrodes, respectively, wherein a predetermined deposition gas isintroduced into a space between said electrode to produce plasma todeposit a silicon oxide film, which contains a predetermined material,on an object to be processed, which is mounted on said first electrode,wherein the frequency of the high-frequency power applied to said firstelectrode is in the range of from 2 MHz to 9 MHz, and the frequency ofthe high-frequency power applied to said second electrode is 50 MHz orhigher.